Arrangement and method in a ship

ABSTRACT

A ship is disclosed which can include a hull, at least one propulsion unit having a propulsion engine, transmission, at least one propeller connected via the transmission to the propulsion engine, and an oscillation sensor situated in a vicinity of the at least one propeller in order to sense cavitation of the at least one propeller. A control unit can control the propulsion engine, the oscillation sensor being connected to the control unit, whereby the output signal of the oscillation sensor is analyzed in the control unit to detect and indicate that a worse degree cavitation is emerging on a display unit at the navigation bridge and/or regulate the rotation speed and/or the power of the propulsion engine.

TECHNICAL FIELD

The invention relates to an arrangement in a ship according to thepreamble of claim 1.

The invention also relates to a method in a ship according to thepreamble of claim 12.

The arrangement and the method can be used in a ship comprising a hull,at least one propulsion engine, transmission means, at least onepropeller connected via the transmission means to the at least onepropulsion engine and a support structure comprising an upper portionbeing supported at the hull, a lower portion, and a front edge, acontrol unit for controlling the at least one propulsion engine.

The ship can have only one propulsion engine or two or more propulsionengines situated at the stern of the ship. The propeller can comprise asingle propeller or two contra-rotating propellers.

The arrangement is suitable to be used especially in large ships e.g.cruisers, tankers transporting oil or liquefied natural gas, vehiclecarriers, container ships and ferries.

BACKGROUND ART

JP patent publication No. 2004182096 discloses a pod-type propulsionapparatus comprising a support structure being pivotably attached to thehull of a ship and a chamber attached to the support structure. Thechamber comprises a motor being connected to a first end of a shaft, thesecond opposite end of the shaft protruding from the front end of thechamber and being connected to a propeller. The rotation angle of thesupport structure is limited when the speed of the ship increases inorder to prevent cavitation.

RU patent publication No. 2009957 discloses a device to reducecavitation in a ship. The propeller at the stern of the ship isconnected via a shaft to a motor within the hull of the ship. There areflexible casings with oscillation drives on the blades of the propeller.A cavitational noise sensor is located on the hull of the ship. Anoscillation frequency control block for the flexible casings isconnected in series with the noise sensor. The propeller shaft is fittedwith a collector with brushes. The sensor generates a signal which isproportional to the acoustic radiations and feeds it as an input signalto the oscillation frequency control block. The oscillation frequencycontrol block in turn generates a return signal to the drives for theflexible oscillation casings in order to reduce cavitational noise tothe minimum.

JP patent publication No. 09136694 discloses automatic speed control ofa water jet pump used in a ship. A pressure sensor detects the deliverypressure of the water jet pump when the ship is moving. A calculatorcalculates the number of revolutions that can be applied to the waterjet pump in order to avoid cavitation generation in water current basedon the output signal of the pressure detector. A signal selectorcompares the calculated number of revolutions and the number ofrevolutions indicated by a steering control unit. The signal selectoroutputs a control signal to a drive motor of the water jet pump byselecting the signal that indicates the smaller number of revolutions.

JP patent publication 09109991 discloses a cavitation prevention typeship fin stabilizer. The stabilizer includes a fin being pivotablysupported to the hull through a shaft. A fin driving mechanism adjustswing angle of the fin by turning the shaft. A water exhaust nozzle atthe lower rear edge of the fin controls cavitation generation of the finwhile cruising. A feed water pump supplies water and discharges waterfrom the exhaust nozzle. An under water microphone situated after thefin, detects noise caused by the cavitation of the fin. A waterinjection controller controls the water injection from the exhaustnozzle by controlling the feed pump based on the noise detection signalof the microphone.

Cavitation occurs when liquid changes its phase into vapour at a certainflow region where local pressure is very low due to high localvelocities. At least four different cavitation types relating to arotating propeller in water can be distinguished: a) tip vortex from thesuction side, which is regarded as normal operation until a certainlevel is exceeded, b) sheet cavitation at suction side, c) tip vortexfrom the pressure side, d) bubble cavitation.

The control bridge is at the stem of the ship i.e. 200 to 400 metersahead of the aft in a big ship. The control bridge is also 15-40 metersabove sea level. This means that the captain or navigating officersitting on the navigation bridge do not normally feel or hear cavitationcaused by the propellers at the aft of the ship. There is thus a need tomake the captain and/or the navigating officer aware of situations whereworse degree cavitation is emerging. Such situations might typicallyoccur when the ship is suddenly accelerated with full power or when thepropulsion unit and/or the ship is turned at big turning angels.

SUMMARY OF THE INVENTION

The object of the invention is an arrangement and method to managesituations where cavitation occurs in a ship.

The arrangement in a ship according to the invention is characterized bythe features in the characterizing portion of claim 1.

The method in a ship according to the invention is characterized by thefeatures in the characterizing portion of claim 12.

The arrangement in a ship according to the invention comprises a hull,at least one propulsion unit comprising a propulsion engine,transmission means, at least one propeller connected via thetransmission means to the propulsion engine, and an oscillation sensorsituated in the vicinity of the at least one propeller in order to senseoscillations caused by cavitation of the at least one propeller. Thearrangement comprises further a control unit for controlling the atleast one propulsion engine, said oscillation sensor being connected tothe control unit, whereby the output signal of the oscillation sensor isanalyzed in the control unit in order to determine whether a worsedegree cavitation is emerging, and indicate that a worse degreecavitation is emerging on a display unit at the navigation bridge and/orregulate the rotation speed and/or the power of the at least onepropulsion engine when worse degree cavitation is emerging.

It is easier to recognize cavitation of the propeller when theoscillation sensor is situated near the origin of the phenomena i.e.near the propeller. When the propulsion unit is about to enter into anunwanted operation phase with harmful worse degree cavitation thecontrol unit sends a warning to a display unit at the navigation bridgeand/or controls the speed and/or the power of the propulsion engine.

When the measurement is done directly from the oscillations caused bythe cavitation of the propeller, the amount of tuning parameters in thesystem is limited to a minimum. The only tuning parameters aresensitivity in the propeller blade frequency, the type of burst and theamplitude. The signal processing of the raw measurements is also rathersimple, which means that the indication of worse case cavitation will befast. The speed ramps of the propulsion unit are normally relative low,which means that there is plenty of time to react before more severecavitation emerges.

First stage tip vortex cavitation is normal in operation e.g. in thecase the ship drives at full speed. First stage tip vortex is alsonormally taken into account in hydrodynamic design and the operationefficiency of the propeller is not harmfully affected by first stage tipvortex. In case the cavitation gets worse, it will be harmful for thewhole propulsion mechanics and may cause instant or long run damage. Aworse class cavitation will result in a collapse of the efficiency ofthe propeller, which decreases the maneuverability of the shipdramatically.

The best position of the oscillation sensor for sensing the tip vortexof the propeller is on a support structure situated behind the propellerin the driving direction of the ship at a place where the tip vortex‘rope’ hits the support structure. The support structure is behind thepropeller in a normal pulling type propulsion unit i.e. in a propulsionunit where the propeller is at the front end of the chamber.

The support structure creates a different density in the hydrodynamicenvironment as the propeller blade passes in front of the supportstructure. The tip vortex and the support structure affect together. Theinteraction between the tip vortex and the support structure will createpropeller blade frequency bursts when the tip vortex gets worse. Thispoint is the borderline to start actions in propulsion control foravoiding more severe cavitation.

There could be a possibility to disabled the control unit in certainconditions by a separate buttom on the steering bridge.

The invention can advantageously be used in large ships e.g. cruisers,tankers transporting oil or liquefied natural gas, vehicle carriers,container ships and ferries. The power of the propulsion unit in suchlarge ships is in the order of at least 1 MW.

BRIEF DESCRIPTION OF THE DRAWINGS

Some specific embodiments of the invention are described in thefollowing in detail with reference to the accompanying figures, inwhich:

FIG. 1 shows an arrangement according to the invention in a shipcomprising a pod propulsion unit.

FIG. 2 shows an arrangement according to the invention in a shipcomprising a rudderpod unit.

FIG. 3 shows an arrangement according to the invention in a shipcomprising a conventional axial propulsion unit.

DETAILED DESCRIPTION OF SOME SPECIFIC EMBODIMENTS

FIG. 1 shows an arrangement according to the invention in a ship with apod propulsion unit.

The arrangement comprises a propulsion unit 100 situated at the stern ofthe ship. The propulsion unit 100 comprises a support structure 10, achamber 20, a propulsion engine comprising a first electric motor 30, ashaft 40, and a propeller 50. The support structure 10 has an upperportion 11, a lower portion 12, a front edge 13 and a rear edge 14. Theupper portion 11 of the hollow support structure 10 is pivotablyattached to the hull 200 of the ship. The chamber 20 is stationaryattached to the lower portion 12 of the hollow support structure 10. Theshaft 40 has a first end which is connected to the first electric motor30 and a second end protruding from the front end 21 of the chamber 20and being connected to the propeller 50. The propeller 50 is thussituated at the front end 21 of the chamber 20. The first electric motor30 can be an induction motor or a synchronous motor. The propeller 50can comprise a single propeller or two contra-rotating propellers. Thedriving direction of the sip is shown by the arrow 51 in the figure.

The propulsion unit 100 comprises further a turning mechanism 60 forturning the propulsion unit 100 in relation to the hull 200 of the shiparound a turning axis Y-Y. The turning mechanism 60 is situated withinthe hull 200 of the ship and comprises a gear rim 61 and a secondelectric motor 62. The shaft 63 of the second electric motor 62 isconnected to a pinion gear 64 and the pinion gear 64 is connected to thecircumference of the gear rim 61. The upper portion 11 of the supportstructure 10 is connected to the gear rim 61. The second electric motor62 will thus rotate the pinion gear 63, which rotates the gear rim 61,which rotates the support structure 10 and thereby the propulsion unit100. The second electric motor 62 can be an induction motor or asynchronous motor. There can naturally be two or more second electricmotors 62 situated around the circumference of the gear rim 61.

The arrangement comprises also a control unit 400 for controlling atleast the first electric motor 30 and alternatively also the second 62electric motor. The control unit 400 will control the first 30 and thesecond 62 electric motors based on the commands from the navigationbridge. The rotation speed of the electric motors 30, 62 can becontrolled e.g. by frequency converters.

The arrangement for cavitation indication comprises further anoscillation sensor 300 being situated on the front edge 13 of thesupport structure 10. The oscillation sensor 300 is situated on thefront edge 13 of the support structure 10 at a height corresponding tothe position of the tip of the propeller 50 blade in the situation whenthe tip of the propeller 50 blade during the rotational movement ispassing in front of the front edge 13 of the support structure 10. Theoscillation sensor 300 is connected to the control unit 400. Thisposition of the oscillation sensor 300 is optimal in view of sensingespecially tip vortex created by the rotating propeller 50.

FIG. 2 shows an arrangement according to the invention in a shipcomprising a rudderpod unit.

The arrangement comprises a propulsion unit 100 situated at the stern ofthe ship. The propulsion unit 100 comprises a support structure 10, achamber 20, a propulsion engine comprising a first electric motor 30, ashaft 40, a propeller 50, and a rudder 70. This arrangement correspondsto the pod arrangement of FIG. 1 except for the rudder 70 and the factthat the support structure 10 is in the rudderpod stationary supportedat the hull 200 of the ship. The rudder 70 is pivotably supported arounda turning axis Y-Y.

FIG. 3 shows an arrangement according to the invention in a shipcomprising a conventional axial propulsion unit. This arrangement has nopod arrangement outside the hull 200 of the ship. The propulsion unit100 comprises a propulsion engine 30 within the hull 200 of the ship, ashaft 40 having a first end connected to the propulsion engine 30 and asecond end extending through an opening at the rear end of the hull 200and being connected to a propeller 50 situated outside the hull 200. Thepropulsion engine 30 could be e.g. a diesel engine or an electric motor.The rudder 70 is situated after the propeller 50 in the drivingdirection S1 of the ship. The rudder 70 is further pivotably supportedaround a turning axis Y-Y.

An oscillation sensor 300 is situated on the front edge 71 of thesupport structure 70 i.e. the rudder 70 at a height corresponding to theposition of the tip of the propeller 50 blade in the situation when thetip of the propeller 50 blade during the rotational movement is passingin front of the front edge 71 of the rudder 70. The oscillation sensor300A could alternatively be attached to the bottom of the hull 200 ofthe ship as also shown in the figure. The position of the oscillationsensor 300A on the hull 200 would in such case be in a radial directionabove the tip of the blade of the propeller 50.

It is advantageous to have the oscillation sensor 300 attached to asupport structure, which is situated behind the propeller 50 in thedriving direction of the ship. The oscillation sensor 300 will in such aposition sense effectively especially tip vortex of the propeller 50. Asuitable support structure to attach the oscillation sensor 300 is e.g.the support structure for the pod or a rudder, but it could be anysupport structure situated behind the propeller 50 in the drivingdirection S1 of the ship. In the case of a pod unit having the propeller50 at the rear end of the chamber 20, a separate support structure isneeded behind the pod for the oscillation sensor 300.

The propeller 50 could be formed of a single propeller or of twocontra-rotating propellers.

The oscillation sensor 300, 300A could be e.g. a pressure sensor, anacoustic sensor, or an acceleration sensor.

When the oscillation sensor 300 is situated on the support structure 10,70 after the propeller 50 in the driving direction S1 of the ship, theoptimal position is at a base height position corresponding to theheight of the tip of the blade of the propeller 50 when the tip of theblade is in an uppermost position. The allowed vertical deviation V1from the base height position is equal to or less than ±25% of thediameter D1 of the propeller 50. An oscillation sensor 300 situated on asupport structure 10, 70 after the propeller 50 measures cavitationpropagating backwards from the propeller 50.

When the oscillation sensor 300A is situated on the hull 200 above thepropeller 50 in the redial direction, the base longitudinal position isexactly above the tip of the propeller 50 blade when the tip of theblade is in an uppermost position. The allowed horizontal deviation H1of the base longitudinal position is equal to or less than 50% of thediameter D1 of the propeller 50. An oscillation sensor 300A situated ina radial position above the propeller 50 measures cavitation propagatingin the radial direction from the propeller 50.

The oscillation sensor 300, 300A must be positioned so that it issensitive to cavitation emerging from the propeller 50.

The control unit 400 could be a separate unit or it could be integratedinto some other control unit in the ship.

The invention could also be implemented in a ship having two or morepropulsion units. E.g. a ship provided with two propulsion units at theaft of the ship would need an oscillation sensor for each propeller anda control circuit for each propulsion motor.

The examples of the embodiments of the present invention presented aboveare not intended to limit the scope of the invention only to theseembodiments. Several modifications can be made to the invention withinthe scope of the claims.

1. An arrangement in a ship comprising: a hull; at least one propulsionunit having a propulsion engine, a transmission, and at least onepropeller connected via the transmission to the propulsion engine; anoscillation sensor situated in a vicinity of the at least one propellerin order to sense oscillations caused by cavitation of the at least onepropeller; and a control unit for controlling the at least onepropulsion engine, said oscillation sensor being connected to thecontrol unit, whereby an output signal of the oscillation sensor will beanalyzed in the control unit in order to determine whether a worsedegree cavitation is emerging, and indicate when a worse degreecavitation is emerging on a display unit at a navigation bridge and/orregulate rotation speed and/or power of the at least one propulsionengine when a worse degree cavitation is emerging.
 2. An arrangementaccording to claim 1, wherein said oscillation sensor is attached to afront edge of a support structure protruding downwards from the hull,said support structure being positioned after the propeller in a drivingdirection of the ship.
 3. An arrangement according to claim 2, whereinthe oscillation sensor is situated on the front edge of the supportstructure at a base height position corresponding to a height of a tipof a blade of the at least one propeller when the tip of the blade is inan uppermost position, with a vertical deviation (V1) which is equal toor less than ±25% of a diameter (D1) of the propeller from the baseheight position.
 4. An arrangement according to claim 1, wherein saidoscillation sensor is situated at a bottom of the hull in a positionabove the propeller.
 5. An arrangement according to claim 4, wherein theoscillation sensor is situated in a radial direction above the propellera base longitudinal position exactly above a tip of a propeller bladewhen the tip of the blade is in an uppermost position, with a horizontaldeviation (H1) of the base longitudinal position which is equal to orless than 50% of a diameter (D1) of the propeller from the baselongitudinal position.
 6. An arrangement according to claim 1,comprising: a support structure pivotably supported at the hull around aturning axis and having a hollow body; and a turning mechanism having atleast one second electric motor for turning the support structure andthereby a chamber relation to the hull of the ship in order to steer theship, wherein: the at least one propulsion engine includes a firstelectric motor situated in the chamber having a front end and a rearend, said chamber being stationary attached to a lower portion of thesupport structure; the transmission includes a shaft having a first endand a second end, said first end of the shaft being connected to thefirst electric motor and said second end of the shaft protruding fromthe front end of the chamber and being connected to the at least onepropeller; and said oscillation sensor is situated at a front edge ofthe support structure behind the at least one propeller in a drivingdirection of the ship.
 7. An arrangement according to claim 1,comprising: a support structure stationary attached to the hull andhaving a hollow body; a rudder situated after the support structure anda chamber in a driving direction of the ship, said rudder beingpivotably supported at the hull around a turning axis; wherein: thepropulsion engine includes a first electric motor situated in thechamber having a front end and a rear end, said chamber being stationaryattached to a lower portion of the support structure; the transmissionincludes a shaft having a first end and a second end, said first end ofthe shaft being connected to the first electric motor and said secondend of the shaft protruding from the front end of the chamber and beingconnected to the propeller; and said oscillation sensor is situated atthe front edge of the support structure behind the at least onepropeller in a driving direction of the ship.
 8. An arrangementaccording to claim 1, comprising: a rudder pivotably supported at thehull around a turning axis, said rudder being positioned after thepropeller in a driving direction of the ship, wherein: the propulsionengine includes a first electric motor or a diesel engine situatedwithin the hull of the ship; the transmission means includes a shafthaving a first end and a second end, said first end of the shaft beingconnected to the propulsion engine and said second end of the shaftprotruding from the rear end of the hull and being connected to thepropeller; and said oscillation sensor is situated at a front edge ofthe rudder behind the at least one propeller in a driving direction ofthe ship.
 9. An arrangement according to claim 8, wherein theoscillation sensor is situated on the front edge of the rudder at a baseheight position corresponding to a height of a tip of blade of the atleast one propeller when the tip of the blade is in an uppermostposition, with a vertical deviation (V1) which is equal to or less than±25% of a diameter (D1) of the propeller from the base height position.10. An arrangement according to claim 1, wherein the ship is a cruiser,a tanker transporting oil or liquefied natural gas, a vehicle carrier, acontainer ship or a ferry.
 11. An arrangement according to claim 1,wherein a power of the at least one propulsion unit is at least 1 MW.12. A method for propulsion of a ship having a hull; at least onepropulsion unit which includes a propulsion engine, a transmission andat least one propeller connected via the transmission to the propulsionengine; and an oscillation sensor situated in a vicinity of the at leastone propeller in order to sense oscillations caused by cavitation of theat least one propeller, wherein the method comprises: measuringcavitation of the at least one propeller with the oscillation sensor;feeding an output signal of the oscillation sensor to a control unit;analyzing the output signal of the oscillation sensor in the controlunit to detect cavitation of the at least one propeller and to determinewhether a worse degree cavitation is emerging; and indicating when aworse degree cavitation is emerging on a display unit at a navigationbridge and/or regulating a rotation speed and/or power of the propulsionengine when a worse degree cavitation is emerging.
 13. An arrangementaccording to claim 3, wherein the ship is a cruiser, a tankertransporting oil or liquefied natural gas, a vehicle carrier, acontainer ship or a ferry.
 14. An arrangement according to claim 5,wherein the ship is a cruiser, a tanker transporting oil or liquefiednatural gas, a vehicle carrier, a container ship or a ferry.
 15. Anarrangement according to claim 3, wherein a power of the at least onepropulsion unit is at least 1 MW.
 16. An arrangement according to claim5, wherein a power of the at least one propulsion unit is at least 1 MW.17. The method according to claim 12, wherein a power of the at leastone propulsion unit is at least 1 MW.